Just by playing the 3rd and 7th of every chord, a guitarist can outline the harmonic movement of a song. When a bass play is involved, they will generally play the root, so there is no need to repeat that. The third will identify a chord as Major or Minor and the seventh will reveal whether the chord is Dominant or even fully Diminished.
I have a pdf chart with all the shell voicings here.
In playing just the "shell" chords (3rd and 7th), you can also eventually use the rest of your fingers to play scales on the upper strings. This is similar to the way a pianist will pieces of a chord with the left hand and melodies with the right hand. It's a technique Lenny Breau pioneered.
One little "trick" for a 2-5 change -- if you take the seventh of a ii chord and move it down a half-step while holding on to the 3rd of the ii, you now have an interval of the 3rd and 7th for a V chord. Try it out!